This invention relates to an apparatus for measuring traces of gas and starts out from a colorimetric measuring arrangement preceded by a reaction chamber in which the gas to be measured is absorbed in a reaction liquid and enters into a color reaction.
The object of the apparatus is to detect in good time physiologically harmful gases, for example in laboratories, chemical production plants or in the environment thereof. In the context of the invention, "in good time" means that, within a few seconds of the dangerous gas appearing, even traces of the gas, i.e. fractions of a milliter per cubic meter of ambient air, can be detected and set off an alarm. Another requirement which an apparatus for measuring traces of gas has to satisfy is that, after the appearance of relatively high concentrations of gas, for example of the order of liters per cubic meter, the apparatus should be ready to measure traces of gas again sufficiently quickly, i.e. within a few minutes (a short regeneration time). Not least, an apparatus for measuring traces of gas is required to operate substantially free from maintenance, i.e an interruption for controlling or correcting should only be necessary after prolonged periods of operation, for example 3 weeks or more, which is also when any auxiliary solutions required should be renewed.
In one known method for the sensitive detection of certain extraneous gases, for example in ambient air, the ambient air is passed through a suitable solution with which the gas component to be detected enters into a characteristic color reaction. To enable fluctuating concentrations of extraneous gases to be continuously recorded--which is a basic requirement for any automatic apparatus for measuring traces of gas--the absorption solution has to be continuously renewed. However, if the gas component to be detected is to be absorbed as completely as possible in the absorption solution, steps must be taken to ensure intimate contact between the gas and the liquid. In conventional apparatus, where the gas is bubbled through the liquid by means of glass frits for example, this can only be achieved by prolonged residence of the gas in the liquid.
As a result of this, the gas may not be detected in good time. In addition, the consumption of absorption solution is high. To reduce the consumption of absorption solution, it would be possible to keep the ratio of the continuous stream of absorption solution (m.sup.3 /h) to the stream of ambient air (m.sup.3 /h) very low, for example at 1:100. In that case, however, hitherto unsolved problems of flow and absorption would arise in conventional apparatus.